One person is missing and two people have been taken to the hospital, authorities said.

While a law-enforcement official told the Associated Press that a crime or terrorism was not suspected, Fox News is reporting that the National Transportation Safety Board is treating the 9:30 incident as an "intentional act."

Some of the IRS offices are on the first floor, which is where the plane hit, according to the Austin American-Statesman.Keep up with a live NBC feed from the crash site: